The present invention pertains to a respiration system with an electrically driven rotary compressor as described, e.g., in U.S. Pat. No. 5,875,783.
Such respiration systems are used especially in the area of medicine and especially in anesthesia apparatus where expensive anesthetics are usually used and recirculation of the exhaled gases and the new added fresh gases is therefore especially desirable. The use of rotary compressors as a gas delivery unit in respiration systems is highly advantageous because correspondingly dimensioned rotary compressors are particularly suitable for rapidly following the spontaneous breathing of a patient by changing the speed of rotation. One drawback of the prior-art rotary compressors in respiration systems is the mechanical mount, which cannot be washed and sterilized. In addition, the bearing lubricant necessary for the mechanical rolling bearings becomes unfit for use during the necessary cleaning. Another drawback of the prior art mechanical mount arises from the noise emissions generated, especially at high speeds of rotation.
Furthermore, a separation between the electric components of the respiration system or the gas delivery unit and the breathing gas is necessary even in open respiration systems without rebreathing because the breathing gas has, in general, an increased oxygen concentration and there is therefore a risk of fire without separation in the case of damage to the insulation.
The object of the present invention is to provide a respiration system which makes possible a low-noise mounting of a gas delivery unit, which unit can also be washed and sterilized and which unit ensures a reliable separation of the breathing gas from the electric components.
One essential advantage of the present invention arises from the fact that the rotary compressor acting as the gas delivery unit is mounted floatingly by means of magnetic interactions and is driven electrically, more specifically electromagnetically in a contactless manner. The service life is practically unlimited due to the floating mount.
In addition, the solution according to the present invention makes it possible to remove, clean, sterilize and reinstall the components swept by the breathing gas so that the respiration system can be used reliably, with low noise, hygienically and conveniently even in recirculation operation.
The special design of the drive according to the present invention includes a magnetically mounted rotary compressor with a can and a stationary seal between the rotary compressor and the stationary components of the mount and the drive.
This can seal must be able to be fluxed magnetically. The seal may generate only weak eddy currents and should be manufactured from a material (ceramic, plastic) which provides a good sliding pairing together with the surface of the rotary compressor. This sliding interaction makes possible the deceleration of the rotary compressor without too much friction and heating in the case of an emergency caused by the failure of the magnetic bearing.
The seal comprises a thin can, which is located on the inner side of the stator and is smooth-walled and preferably cylindrical. This can, which is also called a xe2x80x9cslit tube sealxe2x80x9d in other areas of engineering, is cyclically fluxed by the driving magnetic field; the mechanical components do not perform any relative movements. The seal is not subject to wear and its service life is not limited, either.
In principle, various combinations of active magnetic bearings with electrically energized coils with position sensors and passive magnetic bearings with permanent magnets are possible. It should be noted in this connection that not all six possible degrees of freedom of the rotary compressor with passive magnetic bearings can be floated with permanent magnets. At least one degree of freedom must be actively energized and operated in a position-controlled manner, i.e., there always is at least one active magnetic bearing with electrically energized coils.
It is especially advantageous to design the radial bearings as actively energized and position-controlled magnetic bearings. With this, it is possible to allow the rotary compressor to rotate at high speeds of rotation around its principal axis of inertia rather than around its geometric axis of rotation and thus not to generate any vibrations caused by imbalance.
This imbalance compensation is achieved by taking into account measured values of the position and current. The energization of the active electromagnets, which is variable over time, is performed by means of the measured values.
The stiffness and the damping of the magnetic bearing can thus be influenced, so that a so-called free run is achieved. The controlled parameters of the magnetic bearing control circuit can be adaptively changed as a function of the speed of rotation in a characteristic diagram.
The energization of the active magnetic bearing is favorably switched on and operated before the drive. The rotary compressor floats when stopped and will then be driven floatingly.
Only the position of the rotor is controlled at low speeds of rotation; the state of imbalance is calculated at higher speeds of rotation from the power consumption of the individual radial bearing coils and compensated such that the rotor will no longer rotate around its geometric axis of rotation but around its principal axis of inertia.
The system may use an electric drive of any design that does not require any mechanical contact between the stator and the rotor. A three-phase asynchronous motor with cage rotor or the brushless, electronically commuted d.c. motor with permanent magnet rotor are suitable for use as the electric drive.
In the brushless, electronically commuted d.c. motor, the rotor of the drive is a diametrically magnetized permanent magnet, and the stator of the drive comprises especially three drive coil pairs, which are arranged at an angle of 120xc2x0 in relation to one another such that the field vector of the drive coil magnetic field can be rotated around the axis of the rotor. The position of the rotor permanent magnet is recognized either by means of Hall sensors or, during the rotation, by voltages induced in the drive coils. The individual drive coils are then energized consecutively cyclically such that the rotor rotates. This cyclic energization as a function of the position of the rotor (commutation) takes place without wear by means of semiconductor circuit components.
The magnetic bearing is especially advantageous with respect to the noises which originate to a great extent from the rolling bearings of the gas delivery means in prior-art respirators and anesthesia apparatuses and then disappear completely.
In principle, any rotary compressor, especially radial compressors, but also side-channel compressors or peripheral compressors may be used for gas delivery.
The simple design of the components swept by the gas makes it possible to remove, clean, sterilize and reinstall these components in the field. This allows for the use of a closed respiration system.
There is hermetic separation between the breathing gas with increased oxygen concentration and the current-carrying electric components.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.